1. Field of the Invention
The present invention relates to an audio data transmission technique.
2. Description of the Related Art
Progress of digital technologies is leading to development of various techniques of transmitting video and audio information as digital values. For example, a standard called S/PDIF is becoming popular as a major technique of transmitting an audio signal as a digital signal. This technique is used as an interface to connect an audio playback device such as a CD player to a reception device such as an audio amplifier.
Examine a volume adjustment method when outputting sound. According to a common method, audio data of each channel is transmitted by S/PDIF first. Volume is then adjusted and output on the side of the reception device such as an audio amplifier. In this case, a dial or a remote controller for volume adjustment is prepared on the side of the reception device such as an audio amplifier to make the user adjust volume.
However, certain kinds of audio system configurations require volume adjustment on the transmission device side. In this case, a dial or a remote controller for volume adjustment is prepared on the side of the transmission device to cause the user to adjust volume. Data having a value corresponding to original audio data multiplied by the volume value is transmitted by S/PDIF. The receiving side handles it as data containing the volume value and directly outputs the data.
To transmit the volume value on the transmission device side, for example, a technique disclosed in patent reference (Japanese Patent No. 3085931) is used. The technique disclosed in the patent reference transmits volume data embedded in part of transmission data.
When the method of transmitting data which has a value corresponding to original audio data multiplied by the volume value is used to transmit volume information from the transmission device side, the value obtained by multiplication becomes small as the volume value decreases, resulting in poor S/N ratio.
In the method of transmitting volume data embedded in part of transmission data, one volume value is transmitted using a plurality of frames that are transmission units. For this reason, transmission takes time, and the response delays.